Transfer apparatus

ABSTRACT

An apparatus in which charged particles are preconditioned prior to being transferred from a support surface to a sheet of support material.

PATENTED W Y 74 sum 10F 2 TRANSFER APPARATUS BACKGROUND OF THE INVENTION This invention relates generally to an electrostatographic printing machine, and more particularly concerns an improved transfer system for use therein.

An electrostatographic process involves the creation of an electrostatic latent charge pattern and the reproduction of the charge pattern in viewable form. The field of electrostatography includes electrophotography and electrography. Electrophotography is a class of electrostatography which employs a photosensitive medium to form, with the aid of electromagnetic radiation, an electrostatic latent charge pattern. Electrography is the class of electrostatography which utilizes an insulating medium to form, without the aid of electromagnetic radiation, the electrostatic latent charge pattern. Transfer, which is the act of transferring toner particles deposited on the electrostatic latent charge pattern, in image configuration, to a sheet of support material, may be employed in either of the preceding classes of electrostatography. Hereinafter, an electrophotographic printing machine will be described as an illustrative embodiment of the foregoing processes wherein the transfer system of the present invention may be incorporated. In the process of electrophotographic printing, for example, as disclosed in U.S. Pat. No. 2,297,691 issued to Carlson in 1942, an image bearing member or photosensitive element having a photoconductive insulating layer is charged to a sub stantially uniform potential in order to sensitize its surface. Thereafter, the charged photoconductive surface is exposed to a light image of an original document. As a consequence of the exposure, the charge is selectively dissipated in the irradiated areas in accordance with the light intensity projected onto the photoconductive surface creating an electrostatic latent image thereon. Development of the electrostatic latent image recorded on the photoconductive surface is achieved by bringing a developer mix into contact therewith. Typical developer mixes employed are well known, and generally comprise dyed or colored thermoplastic powders, known in the art as toner particles, which are mixed with coarser carrier granules such as ferromagnetic granules. The developer mix is selected such that the toner particles acquire the appropriate charge relative to the electrostatic latent image recorded on the photoconductive surface. As the developer mix is brought into contact with the photoconductive surface, the greater attractive force of the electrostatic latent image recorded thereon causes the toner particles to move from the carrier granules and adhere thereto. Thereafter, the toner powder image developed on the photoconductive surface may be transferred to a sheet of support material such as paper or a thermoplastic sheet amongst others, to which it may be permanently affixed by any suitable means.

Hereinbefore, the toner powder image has been transferred to the sheet of support material by an electric field created by a corona generator similar to that disclosed in U.S. Pat. No. 2,836,725 issued to Vyverberg in 1958. A corona generator of this type induces transfer to the sheet of support material by spraying a corona discharge having a polarity opposite to that carried by the toner particles on the photoconductive surface, thereby causing the toner particles to be electrostatically transferred to the sheet of support material. This type of corona generator has proven to be ex tremely reliable for transferring a single toner powder image to a sheet of support material. However, such a corona generator does not readily lend itself to transferring multiple toner powder images, in superimposed registration with one another. as is required in multicolor electrophotographic printing.

Other techniques utilized have included an electrically biased transfer roll. The biased transfer roll generates a high voltage discharge in the proximity of the surface of the paper or, it may be applied by means of a conductive cylinder in contact with the paper as disclosed in U.S. Pat. No. 2,807,233 issued to Fitch in 1957. As described therein, a sheet of support material is interposed between the conductive roller and a surface having the toner powder image thereon. A charge of opposite polarity from the toner particles is deposited on the back side of the sheet of support material which attracts the toner powder image thereto. Thus, in this type of apparatus, a direct current supply is required to operate the transfer mechanism.

Many factors influence the quality of the transferred image, the most significant factors being those which effect the uniformity with which the toner powder image is transferred from the photoconductive surface to the sheet of support material. Heretofore, in the process of transferring multi-layered toner powder images, as exemplified by a multi-color electrophotographic printing machine, the transfer of line copy has produced various problems. In particular. when a biased transfer roll is utilized to transfer successive toner powder images in superimposed registration to a sheet of support material, hollow characters frequently occur. Hollow characters may be defined as a toner area wherein substantially only the periphery thereof is transferred while the central portion remains devoid of toner particles. The problem of hollow characters is most pronounced for line copy reproductions, however, hollow characters frequently occur in solid area copy as well.

Accordingly, it is a primary object of the present invention to improve transferring a toner powder image from an image bearing member to a sheet of support material.

SUMMARY OF THE INVENTION Briefly stated, and in accordance with the present invention, there is provided an apparatus for transferring charged particles from a support surface to a sheet of support material.

In the particular apparatus illustrated, this is accomplished by corona generating means operatively associated with a transfer member. Corona generating means, positioned adjacent the support surface, is adapted to apply an alternating charge potential thereto. In this manner, the charged particles disposed on the support surface are preconditioned to readily facilitate the transfer thereof therefrom. Further, in accordance with the present invention, the transfer member has a sheet of support material secured thereto and cooperates electrically with the support surface. This is achieved by electrically biasing the transfer member to a potential of sufficient magnitude to attract the preconditioned charged particles from the support surface to the sheet of support material.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects and advantages of the present invention will become apparent upon reading the following detailed description and upon reference to the drawings, in which: I

FIG. 1 is a schematic perspective view of a multicolor electrophotographic printing machine incorporating the present invention therein;

FIG. 2 is a schematic perspective view of the transfer apparatus of the present invention, as utilized in the FIG. 1 printing machine; and

FIG. 3 is a fragmentary perspective view of the corona generator used in the FIG. 2 transfer apparatus.

While the present invention will be described in connection with a preferred embodiment, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION For a general understanding of the disclosed electrophotographic printing machine in which the present invention may be incorporated, continued reference is had to the drawings, wherein like reference numerals have been used throughout to designate like elements. FIG. 1 schematically illustrates the various components of a printing machine for producing multi-color copies from a colored original. Although the transfer apparatus of the present invention is particularly well adapted for use in an electrophotographie printing machine, it should become evident from the following discussion that it is equally well suited for use in a wide variety of electrostatographic printing machines and is not necessarily limited in its application to the particular embodiment shown herein.

The printing machine illustrated in FIG. I employs an image bearing member having a drum 10 with a photoconductive surface 12 mounted on the exterior circumferential surface thereof. Drum 10 is mounted rotatably within the machine frame. One type of suitable photoconductive material is disclosed in U.S. Pat. No. 3,655,377 issued to Sechak in 1972. A series of processing stations are located such that as drum l rotates in the direction of arrow 14 it passes sequentially therethrough. Drum is driven at a predetermined speed by a drive motor (not shown) relative to the various machine operating mechanisms. The machine logic coordinates the operations at each station with one another to produce the proper sequence of events thereat.

Drum 10 initially moves photoconductive surface 12 through charging station A. Charging station A has positioned thereat a corona generating device indicated generally at 16. Corona generating device 16 extends in a generally transverse direction across photoconductive surface 12. This readily enables corona generating device 16 to charge photoconductive surface 12 to a relatively high substantially uniform potential. The foregoing corona generating device 16 is, preferably, of a type described in U.S. Pat. No. 2,778,946 issued to Mayo in 1957.

Thereafter, drum 10 rotates to exposure station B where a color filtered light image of the original document is projected onto charged photoconductive surface 12. Exposure station B includes thereat a moving lens system, generally designated by the reference numeral l8, and a color filter mechanism shown generally at 20. A suitable moving lens system is disclosed in U.S. Pat. No. 3,062,108 issued to Mayo in 1962, and a suitable color filter mechanism is described in copending application Ser. No. 830,282 filed in 1969. As shown in FIG. 1, an original document 22, such as a sheet of paper, book or the like is placed face down upon transparent viewing platen 24. Lamp assembly 26, filter mechanism 20 and lens 18 move in a timed relation with drum [0 to scan successive incremental areas of original document 22 disposed upon platen 24. In this manner, a flowing light image of original document 22 irradiates photoconductive surface 12. Filter mechanism 20 is adapted to interpose selected color filters into the optical light path. The appropriate color filter operates on the light rays passing through lens 18 to record an electrostatic latent image on photoconductive surface 12 corresponding to a preselected spectral region of the electromagnetic wave spectrum. hereinafter referred to as a single color electrostatic latent image.

After exposure, drum 10 rotates the single color electrostatic latent image recorded on photoconductive surface 12 to development station C. Development station C includes thereat three individual developer units, generally indicated by the reference numerals 28, 30 and 32, respectively. A suitable development station employing a plurality of developer units is disclosed in copending application Ser. No. 255,259 filed in 1972. Preferably the developer units are all of a type referred to generally as magnetic brush developer units. A typical magnetic brush developer unit utilizes a magnetizable developer mix having carrier granules and toner particles therein. The developer mix is continually brought through a directional flux field to form a brush thereof. The single color electrostatic latent image recorded on photoconductive surface 12 is developed by bringing the brush of developer mix into contact therewith. Each of the respective developer units contain discretely colored toner particles corresponding to the complement of the spectral region of the wavelengths of light transmitted through filter 20, e.g., a green filtered electrostatic latent image is rendered visible by depositing green absorbing magenta toner particles thereon, blue and red latent images are developed with yellow and cyan toner particles, respectively.

Drum 10 is, next, rotated to transfer station D where the toner powder image adhering electrostatically to photoconductive surface 12 is transferred to a sheet of support material 34. Support material 34 may be plain paper or a sheet of thermoplastic material, amongst others. Transfer station D includes thereat corona generating means indicated generally at 36, and a transfer member, designated generally by reference numeral 38. Corona generator 36 is excited with an alternating current and is arranged to spray ions on photoconductive surface 12 so as to precondition the toner powder image adhering electrostatically thereto. In this way, the preconditioned toner powder image will more readily be transferred from the electrostatic latent image recorded on photoconductive surface 12 to support material 34 by transfer member 38. Transfer member 38 is a roll adapted to recirculate support material 34 and is electrically biased to a potential of sufficient magnitude and polarity to attract electrostatically the preconditioned toner particles from the latent image recorded on photoconductive surface 12 to support material 34. Transfer roll 38 rotates in synchronism with photoconductive surface 12. Inasmuch as support material 34 is secured releasably thereon for movement in the recirculating path therewith, successive toner powder images may be transferred thereto in superimposed registration with one another. In this case, transfer roll 38 rotates in the direction of arrow 40 at substantially the same angular velocity as photoconductive drum l0. Corona generator 36 and transfer member 38 will be described hereinafter in greater detail with reference to FIGS. 2 and 3.

Support material 34 is advanced from a stack 42 thereof. Feed roll 44, in operative communication with retard roll 46, advances and separates the uppermost sheet from stack 42 disposed on tray 48. The advancing sheet moves into a chute 50 which directs it into the nip between register rolls 52. Thereafter, gripper fingers, indicated generally at 54, mounted on transfer roll 38 secure releasably thereon support material 34 for movement in a recirculating path therewith. With continued reference to FIG. I, after a plurality of toner powder images have been transferred to support mate rial 34, gripper fingers 54 release support material 34 and space it from transfer roll 38. Stripper bar 56 is then interposed therebetween to separate support material 34 from transfer roll 38. Thereafter, endless belt conveyor 58 advances support material 34 to fixing sta tion E. At fixing station E a fuser, indicated generally at 60, coalesces the transferred powder image to support material 34. One type of suitable fuser is described in US. Pat. No. 3,498,592 issued to Moser et al in 1970. After the fusing process, support material 34 is advanced by endless belt conveyors 62 and 64 to catch tray 66 for subsequent removal therefrom by the machine operator.

Although a preponderance of the toner particles are transferred to support material 34, invariably some residual toner particles remain on photoconductive surface 12 after the transfer of the powder image therefrom. The residual toner particles are removed from the photoconductive surface 12 as it moves through cleaning station F. Here, the residual toner particles are first brought under the influence of a cleaning corona generating device (not shown) adapted to neutralize the electrostatic charge remaining thereon. The neutralized toner particles are then mechanically cleaned from photoconductive surface 12 by a rotatably mounted fibrous brush 68. A suitable brush cleaning device is described in US. Pat. No. 3,590,412 issued to Gerbasi in 1971. Rotatably mounted on brush 68 is positioned at cleaning station F and maintained in contact with photoconductive surface 12. In this manner, residual toner particles remaining on photoconductive surface 12 after each transfer operation are readily removed therefrom.

It is believed that the foregoing description is sufficient for purposes of the present application to depict the general operation of a multi-color electrophotographic printing machine embodying the teachings of the present invention.

Referring now to the specific subject matter of the present invention, FIG. 2 depicts the transfer apparatus associated with photoconductive surface 12 of drum 10. Transfer roll 38 includes an aluminum tube 68, preferably. having about a one-fourth inch thick layer of urethane 70 cast thereabout. A polyurethane coating 72, preferably of about 1 mil thick. is sprayed over the layer of cast urethane 70. Preferably. transfer roll 38 has a durometer hardness ranging from about 10 units to about 30 units on the Shore A scale. The resistivity of transfer roll 38, preferably, ranges from about I0 to about l0 ohm-centimeters. A direct current bias voltage is applied to aluminum tube 68 via suitable means such as a carbon brush and brass ring assembly (not shown). The transfer voltage may range from about 1,500 to about 4.500 volts. Transfer roll 38 is substantially the same diameter as drum l0 and is driven at substantially the same speed thereat. Contact between photoconductive surface 12 of drum l0 and transfer roll 38 with support material 34 interposed therebetween, is preferably limited to a maximum of about 1.0 pound linear force. Preferably, transfer roll 38 includes a pair of tapered end bells which are secured to one another by three tie rods. Compression springs limit the tension of the tie rods to about 10 pounds. A pair of spring loaded pivot arms located on a stationary shaft support transfer roll 38 in the electrophotographic printing machine. Solenoids and secondary springs (loaded to about 0.02 pounds per linear inch) lift transfer roll 38 with support material secured thereon against photoconductive surface 12 of drum 10. Transfer roll 38 is moved approximately one-eighth of an inch in order to engage photoconductive surface 12. A spring loaded yoke supports transfer roll 38. This yoke is articulated to permit transfer roll 38 to be adjustably positioned about its own center line and the center line of drum 10. A synchronous speed main drive motor rotates transfer roll 38. This drive is coupled directly to transfer roll 38 by flexible metal bellows 74 which permits the lowering and raising of transfer roll 38. Synchronization of transfer roll 38 and drum 10 is accomplished by precision gears (not shown) coupling the main drive motor to both transfer roll 38 and drum 10.

Referring now to FIG. 3, corona generator 36 is shown therein in detail. Corona generator 36 includes an elongated shield 98 preferably made from a conductive material such as an aluminum extrusion. Elongated shield 98 is substantially U-shaped and may be grounded or, in lieu thereof, biased to a suitable electrical voltage level. A discharge electrode 100 is mounted in the chamber defined by U-shaped shield 98. Discharge electrode 100 is, preferably, a coronode wire approximately 0.0035 inches in diameter and extends longitudinally along the length of shield 98. Coronode wire 100 is made preferably from tungsten having a tungsten oxide coating thereon. Discharge electrode 100 is excited so as to produce a flow of ions therefrom. The ion flow is adapted to precondition the toner particles deposited on the electrostatic latent image of photoconductive surface 12. In this way, transfer roll 38 enhances the efficiency of attracting the toner powder image from the electrostatic latent image recorded on photoconductive surface 12. When the toner particles are pre-conditioned in the foregoing manner, substantially the entire toner powder image is transferred therefrom, hollow characters being substantially eliminated. Preferably, discharge electrode I00 is excited at about 1 l0 micro-amperes and about 4,400 volts RMS, the range being from about micro-amperes at about 3,000 volts RMS to about 200 micro-amperes at about 5,000 volts RMS. The alternating current output from coronode wire 100 to photoconductive surface 12 with the toner powder thereon ranges from about 3.0 to about 5.0 micro-amperes, and is preferably about 4.0 micro-amperes.

ln recapitulation, it is apparent that a transfer roll cooperating with an alternating current corona generator substantially minimizes hollow characters and insures that substantially the entire area of the toner powder image is transferred to the support material. Although the exact scientific reason is presently unknown, it has been found experimentally that the utilization of an alternating current corona generator spraying ions on the toner powder image facilitates transfer thereof by an electrically biased transfer roll. In particular, this has been found to be particularly significant when a plurality of toner powder images are transferred from the photoconductive surface to the support material, in superimposed registration with one another. The foregoing transfer apparatus reduces hollow characters on the support material, and transfers substantially the entire area developed on the electrostatic latent image to the support material.

It is, therefore, evident that there has been provided in accordance with this invention an apparatus for transferring a toner powder image developed on a photoconductive surface to a sheet of support material that fully satisfies the objects, aims and advantages set forth above. While this invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all alternatives, modifications and variations as fall within the spirit and broad scope of the appended claims.

What is claimed is:

1. An apparatus for transferring charged particles from a support surface to a sheet of support material, including:

corona generating means disposed adjacent the support surface for applying an alternating charge potential to the support surface and the charged particles adhering thereto so as to substantially neutralize the attractive charge therebetween, thereby facilitating the transfer of the particles from the support surface, said corona generating means comprising an elongated shield defining an open-ended chamber and a corona discharge electrode mounted in the shield chamber;

means for energizing the discharge electrode of said corona generating means with an alternating current;

a transfer member operatively associated with said corona generating means and having the sheet of support material secured thereto, said transfer member comprising a substantially cylindrical core of electrically conductive material and a plurality of layers of resilient material entrained about the cylindrical core with at least one layer of resilient material being substantially in contact therewith; and

means for applying an electrical biasing potential to the cylindrical core of said transfer member, said transfer member cooperating electrically with the support surface and being biased electrically to a potential of sufficient magnitude to attract the particles to the sheet of support material.

2. An apparatus as recited in claim 1, wherein:

said corona generator means shield includes a substantially U-shaped member; and

said corona generator means discharge electrode includes a conductive coronode wire mounted in the chamber of the shield and extending substantially in a longitudinal direction along the length of the shield.

3. An apparatus as recited in claim 2, wherein said energizing means excites said coronode wire at an alternating current ranging from about microamperes RMS to about 200 micro-amperes RMS. and preferably being about 1 l0 micro-ampcres RMS. said energizing means exciting said coronode wire at an alternating voltage ranging from about 3,000 volts RMS to about 5,000 volts RMS, and preferably being about 4,400 volts RMS.

4. An apparatus as recited in claim 3, wherein said coronode wire generates an alternating current output to the support surface having the charged particles thereon ranging from about 3.0 micro-amperes to about 5.0 micro-amperes, and being preferably about 4.0 micro-amperes.

5. An apparatus as recited in claim 4, wherein the resistivity of said transfer member ranges from about l0 ohm-centimeters to about l0 ohm-centimeters.

6. An apparatus as recited in claim 5, wherein the hardness of said transfer member ranges from about 10 to about 30 units on a Shore A durometer hardness scale.

7. An apparatus as recited in claim 6, wherein said bias applying means energizes said transfer member at a voltage ranging from about 1,500 volts to about 4,500 volts.

8. An apparatus as recited in claim 7, wherein the resilient layers of said transfer member include: a first layer formed of a urethane material; and a second layer entrained about said first layer and formed of a polyurethane material.

9. An electrostatographic printing machine of the type wherein charged toner particles are transferred to a sheet of support material forming thereon a copy of the original document being reproduced, including:

an image bearing member having toner particles deposited thereon in image configuration;

corona generating means disposed adjacent said image bearing member for applying an alternating charge potential to said image bearing member and the charged toner particles adhering thereto so as to substantially neutralize the attractive charge therebetween, thereby facilitating the transfer of the toner particles from said image bearing memher, said corona generating means comprising an elongated shield defining an open-ended chamber and a corona discharge electrode mounted in the shield chamber;

means for energizing the discharge electrode of said corona generating means with an alternating current; transfer member operatively associated with said corona generating means and having the sheet of support material secured releasably thereto, said transfer member comprising a substantially cylindrical core of electrically conductive material and a plurality of layers of resilient material entrained about the cylindrical core with at least one layer of resilient material being substantially in contact therewith; and

means for applying an electrical biasing potential to the cylindrical core of said transfer member, said transfer member cooperating electrically with said image bearing member and being biased electrically to a potential of sufficient magnitude to attract the toner particles to the sheet of support material.

10. A printing machine as recited in claim 9, wherein:

said corona generator means shield includes a substantially U-shaped member; and

said corona generator means discharge electrode includes a conductive coronode wire mounted in the chamber of the shield and extending substantially in a longitudinal direction along the length of the shield.

11. A printing machine as recited in claim 10, wherein said energizing means excites said coronode wire at an alternating current ranging from about 80 micro-amperes RMS to about 200 micro-amperes RMS, and preferably being about 110 micro-amperes RMS, said energizing means exciting said coronode wire at an alternating voltage ranging from about 3,000 volts RMS to about 5,000 volts RMS, and preferably being about 4,400 volts RMS.

12. An apparatus as recited in claim 11, wherein said coronode wire generates an alternating current output to said image bearing member having the charged particles thereon ranging from about 3.0 micro-amperes to about 5.0 micro-amperes. and being preferably about 4.0 micro-amperes.

13. A printing machine as recited in claim 12, wherein the resistivity of said transfer member ranges from about 10* ohm-centimeters to about l0 ohmcentimeters.

l4. A printing machine as recited in claim 13, wherein the hardness of said transfer member ranges from about l0 to about 30 units on a Shore A durometer hardness scale.

15. A printing machine as recited in claim 14. wherein said bias applying means energizes said transfer member at a voltage ranging from about l .500 volts to about 4,500 volts.

16. A printing machine as recited in claim 15, wherein the resilient layers of said transfer member include:

a first layer formed of a urethane material; and

a second layer entrained about said first layer and formed of a polyurethane material.

=l =i l 

1. An apparatus for transferring charged particles from a support surface to a sheet of support material, including: corona generating means disposed adjacent the support surface for applying an alternating charge potential to the support surface and the charged particles adhering thereto so as to substantially neutralize the attractive charge therebetween, thereby facilitating the transfer of the particles from the support surface, said corona generating means compRising an elongated shield defining an open-ended chamber and a corona discharge electrode mounted in the shield chamber; means for energizing the discharge electrode of said corona generating means with an alternating current; a transfer member operatively associated with said corona generating means and having the sheet of support material secured thereto, said transfer member comprising a substantially cylindrical core of electrically conductive material and a plurality of layers of resilient material entrained about the cylindrical core with at least one layer of resilient material being substantially in contact therewith; and means for applying an electrical biasing potential to the cylindrical core of said transfer member, said transfer member cooperating electrically with the support surface and being biased electrically to a potential of sufficient magnitude to attract the particles to the sheet of support material.
 2. An apparatus as recited in claim 1, wherein: said corona generator means shield includes a substantially U-shaped member; and said corona generator means discharge electrode includes a conductive coronode wire mounted in the chamber of the shield and extending substantially in a longitudinal direction along the length of the shield.
 3. An apparatus as recited in claim 2, wherein said energizing means excites said coronode wire at an alternating current ranging from about 80 micro-amperes RMS to about 200 micro-amperes RMS, and preferably being about 110 micro-amperes RMS, said energizing means exciting said coronode wire at an alternating voltage ranging from about 3,000 volts RMS to about 5,000 volts RMS, and preferably being about 4,400 volts RMS.
 4. An apparatus as recited in claim 3, wherein said coronode wire generates an alternating current output to the support surface having the charged particles thereon ranging from about 3.0 micro-amperes to about 5.0 micro-amperes, and being preferably about 4.0 micro-amperes.
 5. An apparatus as recited in claim 4, wherein the resistivity of said transfer member ranges from about 108 ohm-centimeters to about 1011 ohm-centimeters.
 6. An apparatus as recited in claim 5, wherein the hardness of said transfer member ranges from about 10 to about 30 units on a Shore A durometer hardness scale.
 7. An apparatus as recited in claim 6, wherein said bias applying means energizes said transfer member at a voltage ranging from about 1,500 volts to about 4,500 volts.
 8. An apparatus as recited in claim 7, wherein the resilient layers of said transfer member include: a first layer formed of a urethane material; and a second layer entrained about said first layer and formed of a polyurethane material.
 9. An electrostatographic printing machine of the type wherein charged toner particles are transferred to a sheet of support material forming thereon a copy of the original document being reproduced, including: an image bearing member having toner particles deposited thereon in image configuration; corona generating means disposed adjacent said image bearing member for applying an alternating charge potential to said image bearing member and the charged toner particles adhering thereto so as to substantially neutralize the attractive charge therebetween, thereby facilitating the transfer of the toner particles from said image bearing member, said corona generating means comprising an elongated shield defining an open-ended chamber and a corona discharge electrode mounted in the shield chamber; means for energizing the discharge electrode of said corona generating means with an alternating current; a transfer member operatively associated with said corona generating means and having the sheet of support material secured releasably thereto, said transfer member comprising a substantially cylindrical core of electrically conductive material aNd a plurality of layers of resilient material entrained about the cylindrical core with at least one layer of resilient material being substantially in contact therewith; and means for applying an electrical biasing potential to the cylindrical core of said transfer member, said transfer member cooperating electrically with said image bearing member and being biased electrically to a potential of sufficient magnitude to attract the toner particles to the sheet of support material.
 10. A printing machine as recited in claim 9, wherein: said corona generator means shield includes a substantially U-shaped member; and said corona generator means discharge electrode includes a conductive coronode wire mounted in the chamber of the shield and extending substantially in a longitudinal direction along the length of the shield.
 11. A printing machine as recited in claim 10, wherein said energizing means excites said coronode wire at an alternating current ranging from about 80 micro-amperes RMS to about 200 micro-amperes RMS, and preferably being about 110 micro-amperes RMS, said energizing means exciting said coronode wire at an alternating voltage ranging from about 3,000 volts RMS to about 5,000 volts RMS, and preferably being about 4,400 volts RMS.
 12. An apparatus as recited in claim 11, wherein said coronode wire generates an alternating current output to said image bearing member having the charged particles thereon ranging from about 3.0 micro-amperes to about 5.0 micro-amperes, and being preferably about 4.0 micro-amperes.
 13. A printing machine as recited in claim 12, wherein the resistivity of said transfer member ranges from about 108 ohm-centimeters to about 1011 ohm-centimeters.
 14. A printing machine as recited in claim 13, wherein the hardness of said transfer member ranges from about 10 to about 30 units on a Shore A durometer hardness scale.
 15. A printing machine as recited in claim 14, wherein said bias applying means energizes said transfer member at a voltage ranging from about 1,500 volts to about 4,500 volts.
 16. A printing machine as recited in claim 15, wherein the resilient layers of said transfer member include: a first layer formed of a urethane material; and a second layer entrained about said first layer and formed of a polyurethane material. 